The present invention relates to a sheet supply apparatus for sequentially supplying sheets stacked on a sheet supply tray of a copier, etc., to a predetermined position for processing, and more particularly to technology for detecting a size of the sheets stacked on the sheet supply tray.
Conventionally, a sheet supply apparatus of a sheet feeding apparatus mounted on an image forming apparatus such as a copier, a facsimile and a printer is provided with a sheet supply tray for stacking sheets, feed rollers for feeding the sheets from the sheet supply tray, and supply rollers for separating and supplying the sheets one at a time.
There is a sheet supply apparatus in which a sheet supply portion separates sheets on a sheet supply tray into a single sheet and turns the sheets over to supply to a platen, then a transport unit transports the sheets to a predetermined position on the platen for reading. After being read, the sheets are turned over again at a discharge portion to be discharged to a discharge tray.
In such a sheet supply apparatus, the sheet supply tray and discharge tray are overlapped so as to reduce an installation space as opposed to configurations in which both trays are arranged horizontally next to each other. However, it is sometimes difficult to remove the sheets on the discharge tray depending on a position of the sheet supply tray, or difficult to visually confirm the discharged sheets.
In order to resolve these problems, there has been a configuration in which an auxiliary tray is provided for supporting sheets larger than A4 or B4. The auxiliary tray can be pulled out from the sheet supply tray. The auxiliary tray is usually stored in a storage position, and pulled out when necessary.
In general, the sheet supply apparatus is provided with size sensors for detecting a size of the sheets mounted on the sheet supply tray. The size sensors detect the size of the sheets stacked on the sheet supply tray, and send a signal to a main unit such as a copier. Accordingly, it is possible to perform a preliminary operation such as supplying a copier sheet in the main unit or a preparatory operation for processing an image before reading the image on the sheets, thereby improving the processing efficiency of the overall system.
However, in the case that the size sensors are disposed on the auxiliary tray for detecting the size of the sheets, when the auxiliary tray is not completely pulled out, it is possible to detect the size incorrectly. Also, when the auxiliary tray is stored, it is not possible to detect the size of the sheets on the sheet supply tray. Therefore, the processing efficiency of the overall image forming apparatus including an image reading apparatus is decreased.
In view of the problems described above, an object of the present invention is to provide a sheet supply apparatus that can detect the size of the sheets even when the sheet supply apparatus is provided with the auxiliary tray, thereby improving the processing efficiency.
Further objects and advantages of the invention will be apparent from the following description of the invention.